1. Field of the Invention
This invention relates generally to solid-state thermoelectric Peltier effect heating and cooling devices for thermally treating the human body, and more particularly to such a device that has a carbon foam heat sink which facilitates miniaturization, and provides greater surface area per unit volume and significantly greater heat transfer efficiency than conventional finned heat sinks.
2. Brief Description of the Prior Art
Peltier effect thermoelectric heat pumping devices that are used for thermally treating (cooling or heating) the human body are known in the art. Such solid-state heat pumping devices typically contain a Peltier module, a heat sink and a fan. Most prior art devices utilize a heat sink that is comprised of a block of aluminum or copper having protruding fins from which heat is removed by radiation, natural convection or the forced convection of a fan. These types of prior art heat sinks are bulky and heavy and generally constitute the largest component of the heat pump device and thereby render the devices unsatisfactory for applications having size or weight restrictions. A fan placed in close proximity of the heat sink also adds to the size of the device.
Klein, U.S. Pat. No. 4,930,317 discloses a hot/cold therapy device having a hot/cold pad assembly remotely connected to a control module. The hot/cold pad assembly includes a flexible pad filled with a convection (gel) or conduction (laminated metal, rubber impregnated with metal particles, etc.), or combination thereof (a conductive metal layer immersed in a gel). A thin plate of conductive material (copper) forms an extension of the cold plate of a thermoelectric heat pump, both of which are in thermal contact with the pad. A finned air-cooled heat sink is mounted in a housing or shroud which is connected by a flexible umbilical line to the control module. The control module includes a fan for drawing or blowing air through the shroud to maintain the temperature difference between the finned heat sink and attached plate of the thermoelectric heat pump element. The control module includes temperature setting and adjusting mechanisms with a display for displaying the pad temperature detected by a temperature sensing transducer. Other embodiments include placement of the fan within the shroud to cool the heat sink, using a water cooled block heat sink connected to a water reservoir, radiator, and water pump contained in the control module together with a fan to cool the radiator.
Galvan et al, U.S. Pat. No. 5,197,294 discloses a miniaturized thermoelectric apparatus for air conditioning a protective body suit. The apparatus is an assembly made up of a Peltier effect thermoelectric device, in the form of bimetallic or plurimetallic plates connected to a low voltage D.C. power supply, the opposed cold and hot surface of which are in contact with respective finned heat exchangers. The assembly is contained in a housing in which two distinct and separate conduits are provided for the forced flow of air through the respective ones of the finned heat exchangers.
Arnold, U.S. Pat. No. 5,970,718 discloses a personal heat control apparatus having an outer casing that accommodates a Peltier-effect unit, one or more batteries and a timing switch for selective energization of the unit. The casing is releasably attached to a part of a person""s body, e.g. the wrist, by a strap with a cooling surface cooled by the unit in contact with the body part to enhance heat transfer between the person""s body and the surrounding air for comfort and refreshment purposes when the unit is energized. Heat generated in the unit is dispersed through the outer casing, which serves as the heat sink. The surface area of the heat sink (casing) may be several times the size of the cooling surface, e.g. five times larger, to promote rapid heat dissipation.
Johnston, U.S. Pat. No. 6,023,932 discloses a portable topical heat transfer device for topically cooling an animal or human which comprises a thermoelectric unit having a cold side and a warm side, a DC source which is connected to the thermoelectric unit, a finned heat sink which is mounted in a heat conductive relationship with the warm side of the thermoelectric unit, a fan for removing heat from the heat sink, and a strap or the like for securing the device to the body of the wearer. The heat sink comprises the main body portion of the device and includes a series of fins and channels.
Taylor et al, U.S. Pat. No. 6,125,636 discloses a self-contained personal cooling and/or heating device that includes a heat-dissipating member which fits around a portion of a user""s body. A Peltier thermo-voltaic module operated with low voltage at relatively low current is thermally coupled to the rear surface of the member, and the rear surface of the module is provided with a large surface area, preferably augmented by a finned heat sink. A fan directs ambient air onto this rear module surface or heat sink. The device preferably is controlled by a microprocessor that biases the module with a pulse train, samples temperature across the module during an off-portion of the pulse train, and uses sampled signals to vary duty cycle and/or amplitude of the voltage across the module to finely control temperature. The device preferably is controlled by a self-contained battery source whose polarity across the module is user-changeable, causing the device to heat or cool the user as desired.
Most of these prior art devices are unsatisfactory for applications having size or weight restrictions because they utilize one or more finned heat sinks formed of aluminum or copper which are bulky and heavy and generally constitute the largest component of the device, or they utilize a casing or housing of relatively large surface area that serves to dissipate heat. Some of these devices also utilize a fan in close proximity to the heat sink which also adds to the size of the device.
The present invention overcomes the size and weight limitations of the prior art and is distinguished over the prior art in general, and these patents in particular, by a miniaturized Peltier effect solid-state heating and cooling device for thermally treating the human body that utilizes a carbon foam heat sink of porous open cell structure which provides greater surface area per unit volume and significantly greater heat transfer efficiency than conventional finned heat sinks. Miniaturization is further facilitated by placing the air pump and power supply unit remote from the thermoelectric Peltier effect heating and cooling unit to extract and dispose of heat collected from the carbon foam heat sink.
The carbon foam heat sink material utilized in the present invention is, preferably, a recently developed new material known as xe2x80x9cPocoFoamxe2x80x9d(copyright) marketed by Poco Graphite, Inc., of 1601 South Street, Decatur, Tex. 76234, which is produced by a patented foaming process disclosed in U.S. Pat. Nos. 6,033,506 and 6,037,032 issued to James W. Klett et al., and which are hereby incorporated by reference to the same extent as if fully set forth herein
This new material is a high thermal conductivity porous foam which allows the transfer of a large volume of thermal energy. The carbon or graphite aligned ligament structure conducts heat better than copper or aluminum. Its porous structure gives it an enormous surface area, such as two square meters per cubic centimeter of material. That is to say, a sugar cube sized piece of this material would have the surface area of forty-two square feet and weigh half a gram. Air is passed through its interconnecting porous network wherein heat is removed. In comparison, a sugar cube sized aluminum heat sink may have a surface area of a few square inches and may only transfer a minute amount of heat.
It is therefore an object of the present invention to provide a miniaturized Peltier effect solid-state heat pump for thermally treating the human body, which is sufficiently small to be worn and concealed beneath practically any type of hardhat, helmet, hazardous material suit, industrial or occupational wear, costumes, sporting or casual wear.
It is another object of this invention to provide a miniaturized Peltier effect solid-state heat pump for thermally treating the human body that utilizes a carbon foam heat sink which is significantly smaller and lighter in weight than conventional finned heat sinks.
Another object of this invention is to provide a miniaturized Peltier effect solid-state heat pump for thermally treating the human body that utilizes a carbon foam heat sink of porous open cell structure to provide greater surface area per unit volume and significantly greater heat transfer efficiency than conventional finned heat sinks.
A further object of this invention is to provide a miniaturized Peltier effect solid-state heat pump for thermally treating the human body that utilizes a carbon foam heat sink of porous open cell structure and a remote heat extraction and discharge unit that extracts and discharges collected heat from the heat sink.
A still further object of this invention is to provide a miniaturized Peltier effect solid-state heat pump for thermally treating the human body that utilizes a carbon foam heat sink which is simple in construction, inexpensive to manufacture, and rugged and reliable in operation.
Other objects of the invention will become apparent from time to time throughout the specification and claims as hereinafter related.
The above noted objects and other objects of the invention are accomplished by a personal thermoelectric Peltier effect heating and cooling device for heating or cooling a portion of a user""s body that utilizes a porous carbon foam heat sink secured to one surface of a Peltier thermovoltaic member. The heat sink is formed of a thermally conductive open cell foam medium through which air can pass and is partially enclosed by a shroud and a surrounding air filter. The opposed surface of the Peltier thermovoltaic member is secured to a flexible thermal transfer band that is releasable strapped to a portion of the user""s body. A miniature vacuum air pump and a battery are contained in a small enclosure that is releasably secured on another portion of the user""s body remote from the thermal transfer band. A flexible tubular conduit connects the air pump inlet to the shroud and draws ambient air through the thermally conductive open cell foam medium. Electrical leads connected between the battery and the Peltier thermovoltaic member extend through the flexible tubular conduit. An on/off switch on the enclosure selectively energizes the air pump and the Peltier thermovoltaic member. A polarity reversing switch on the enclosure supplies selected polarized electrical energy to the Peltier thermovoltaic member for cooling or heating. In a preferred embodiment, the open cell foam medium is a lightweight, porous graphite foam with an average pore diameter of approximately 350 microns (approximately 0.0138 inches) and has an effective heat exchanging surface area greater than about 4 m2/g (about 19500 ft2/lb). Thus the present invention provides significantly greater heat transfer efficiency than devices utilizing conventional finned heat sinks. Miniaturization is further facilitated by placing the air pump and power supply unit remote from the thermoelectric Peltier effect heating and cooling unit to extract and dispose of heat collected from the carbon foam heat sink.